The present invention relates to a ribbon feed mechanism for printing machines and more particularly relates to a toothed wheel rigidly mounted on a drive shaft at an angle relative to a plane perpendicular to the axis of the drive shaft for improving ribbon feed consistency.
A known ribbon feed mechanism for printing machines has a toothed wheel rigidly mounted on a drive shaft in a plane perpendicular to the axis of the drive shaft. The toothed wheel penetrates the outer convolutions of a roll of film ribbon for feeding the film ribbon. This ribbon feed mechanism is disclosed in U.S. Pat. No. 2,127,812 issued on Aug. 23, 1938 and invented by William A. Gabrielson.
Another known ribbon feed mechanism for printing machines includes a ribbon cartridge which has supported therein a drive shaft, a toothed wheel rigidly mounted on the drive shaft in a plane perpendicular to the axis of the drive shaft and a roll of film ribbon. The toothed wheel penetrates the outer convolutions of the roll of film ribbon for feeding the film ribbon. This ribbon feed mechanism is disclosed in U.S. Pat. No. 4,337,001 issued on June 29, 1982, invented by Samuel D. Cappotto and has the same assignee as the present invention.
Each of these known ribbon feed mechanisms has a disadvantage in that having the toothed wheel mounted on the drive shaft in a plane perpendicular to the axis of the drive shaft causes the teeth of the toothed wheel to penetrate the outer convolutions of the roll of film ribbon in substantially the same location relative to the ribbon width. The teeth normally penetrate several layers of outer convolutions of the film ribbon. When the ribbon feed mechanism is operated during relatively high speed printing (over 20 characters per second), such as printers operated from a memory source, the teeth will penetrate the ribbon in some of the same holes several times, due to the holes forming a substantially straight line pattern, as the ribbon winds on to the take-up spool which causes elongation of the holes. When the holes become elongated, the teeth will not consistently feed the ribbon with equal length increments which causes some characters to overstrike on the ribbon. Over striking of characters on some types of commonly used film ribbons will cause characters to be only partially printed.